412 DISCOVERY REPORTS 



From the foregoing material one may conclude that through the greater part of the 

 year the testis is in a comparatively quiescent condition. As will be shown later pairing 

 may take place exceptionally at almost any time of year, and this may account for the 

 slow but steady production of spermatozoa during the other months. 



It is true that there are one or two cases of whales in which the testis appeared to 

 be producing spermatozoa comparatively rapidly at times when the majority are 

 quiescent, e.g. Nos. 374 (January), 471 (January), and 552 (February), but the activity 

 of the testis in April and May, in comparison with its condition in other months, is 

 quite unmistakable. No material is available for June, but no doubt the conditions 

 in this month are similar to those for May. 



The bearing of these observations on the question of the season at which pairing 

 takes place will be considered in a later section. 



BREEDING AND GROWTH 



SOURCES OF INFORMATION ON BREEDING 



The study of the reproductive processes and breeding habits of whales constitutes 

 probably the most important part of the work concerned with direct observations 

 on whales. The sources from which information may be obtained on this subject are 

 included mainly among (i) the examination of the reproductive organs themselves, 

 (2) the study of the occurrence of foetuses, and (3) the correlation of the seasonal move- 

 ments and other habits of whales, with the reproductive processes. 



The difficulty of obtaining any direct evidence on the breeding of whales has already 

 been pointed out, and it may be said that the investigation of evidence from one source 

 alone, such as the lengths of foetuses at different times, does not provide quite adequate 

 information. It is necessary to put together the evidence from all sources in an endeavour 

 to build up, so to speak, as much as possible of the life history and reproductive cycle 

 of the whales under consideration. 



In the first place, it must be explained that nearly all the conclusions which are to be 

 drawn on the breeding habits of whales ultimately rest on the assumption that there is 

 an annual migration of these whales towards the equator in winter into warmer waters 

 for purposes of breeding, and southwards in summer into colder waters where food is 

 more plentiful. It is not necessary to assume that this rule is rigidly adhered to by all 

 the whalebone whales, but it is sufficient if it can be shown that there is at least a general 

 tendency in the south for a northward breeding movement in winter and a southward 

 feeding movement in summer. This annual migration has been fairly well established 

 by other investigators, but as it is of considerable importance here it will be best at 

 this point to give some attention to the evidence supporting it. 



To begin with, there is the evidence from the quantities of whales caught at whaling 

 stations in different latitudes at different seasons. Briefly it may be said that at the 

 southern stations, such as those in South Georgia, which is a relatively cold region, the 



